Occupancy sensors are designed to save energy by detecting the presence of a moving object in an area of coverage and switching a light source on and off depending upon the presence of the moving object. For example, when motion is detected within the area of coverage, the light source is turned on. Alternatively, when motion is not detected indicating that the area of coverage is not occupied, the light source is turned off after a predetermined period of time. Occupancy sensors thus facilitate electrical energy savings by automating the functions of a light switch or an electrical outlet.
Occupancy sensors can be used to monitor any of a variety of locations, including office spaces, hotel rooms, stairwells, and the like. Where occupancy sensors are used to control lighting in spaces such as stairwells or other areas where visibility is important, occupancy sensor failure can present a safety hazard because lighting may remain off even when a person has entered the area. To address such potential safety hazards, the National Fire Protection Association (NFPA) 101 Life Safety Code requires that low level ambient lighting be provided in stairwells and other areas where visibility is important even when they are not occupied. Thus, one high-intensity light may provide normal space illumination when motion is detected, while a second, low-intensity, light may provide the low level ambient lighting when motion is not detected. Such arrangements provide energy savings, along with desired safety, because the high-intensity light is illuminated only when the space is occupied, while the low-intensity light provides desired safety illumination levels when the space is not occupied.
A disadvantage of using a high-intensity light and a low-intensity light configuration is the potential for the low-intensity ambient light failing, and subsequently the occupancy sensor malfunctioning so that the high-intensity light does not turn on when the space is occupied. Furthermore, a high-intensity light and a low-intensity light configuration does not provide a way to determine if the low-intensity light has failed other than if a person enters the space and visually determines that both the high-intensity light and the low-intensity light have not turned on. Thus, as will be appreciated, a high-intensity light and a low-intensity configuration would provide a “safe” configuration only if the low-intensity light is functioning properly.
It would, therefore, be desirable to provide a fail-safe arrangement for an occupancy sensor that ensures that a space is illuminated even in the event that the low-intensity light fails. It would also be desirable to provide an arrangement in which failed low-intensity lighting can be automatically identified so that repair can be scheduled in an efficient manner.
It would further be desirable to provide an occupancy sensor having a variety of advanced functionality. For example, current occupancy sensors include configuration features that can only be accessed by a user having direct physical access to the sensor. For sensors positioned in elevated locations this is inconvenient and can pose a safety hazard as it requires the user to be on a ladder. It would therefore be desirable to provide an occupancy sensor that is remotely configurable so that a user standing on the ground can remotely configure one or more occupancy sensors positioned on a ceiling, high wall, or the like.
In addition, current applications that employ multiple occupancy sensors (e.g., large halls, multiple entrance rooms, or stairways), do so using a plurality of low voltage occupancy sensors. Low voltage occupancy sensors are sensors without a relay, and as such they cannot directly control a connected load. Rather, they must be connected to a separate load control device such as a power pack, which switches the load on/off in response to a signal from the occupancy sensors. It would be desirable to provide a line voltage occupancy sensor with a built-in load control feature as well as interfaces to a plurality of low voltage occupancy sensors so that the line voltage sensor can act as a load control device for the low voltage sensors.
Moreover, current occupancy sensors are often coupled to building automation systems or building management systems (BMS). Under emergency conditions (e.g., fire), the BMS acts to override the normal operation of the occupancy sensors to ensure that the lights stay on to aid emergency personnel, such as firemen as well as security personnel. Coupling of the occupancy sensors to the BMS is often accomplished through external interface units. As will be appreciated, providing separate external interface units can result in increased system cost. It would be desirable, therefore, to provide an occupancy sensor with an integral interface for connecting to a BMS to enable the BMS to override the normal operation of the sensor under emergency conditions.
In addition, passive infrared (PIR) occupancy sensors operate by sensing a body having a heat signature in excess of background infrared (IR) levels. As the ambient temperature of a monitored space rises, the difference between human body temperature and the ambient temperature decreases, and as a result PIR occupancy sensors can be less able to differentiate the heat of a human body from the heat of the surroundings. This may be particularly acute where the occupancy sensor is deployed in a hot climate where the temperature of the monitored space can be very high if air conditioning is not in use. It would be desirable to provide an occupancy sensor with an active temperature compensation feature to ensure that passive infrared (PIR) sensors appropriately indicate an occupancy condition even at high ambient temperatures. In addition, it would be desirable to provide an occupancy sensor with an automatically adjustable coverage area, so as to eliminate the need for masking inserts.